Method for continuously regulating or tracking a position of a welding torch or a welding head

ABSTRACT

The invention describes a method of continuously controlling and tracking a position of a welding torch ( 10 ) and welding head relative to a weld seam to be produced on a workpiece ( 16 ), whereby the welding torch ( 10 ), spaced at a distance apart from a workpiece ( 16 ) and the weld seam, effects a pendulum motion which is superimposed on its linear welding motion, during which state variables, in particular an ohmic resistance or a current and/or a voltage, are detected as they change in time. The lateral deviation of the welding torch ( 10 ) from the weld seam, in particular from the welding line centre, and/or the height of the welding torch ( 10 ) above the workpiece ( 16 ) and the welding head are derived from the detected actual values and signals in order to control and track the position of the welding torch ( 10 ). Depending on periodically occurring process phases of a welding process, the measurement value detection routine for at least one measurement signal, in particular to detect the state variable, is run at fixed instants and/or states of the periodically recurring process phases of the welding process.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of Austrian ApplicationNo. A580/2000 filed Apr. 5, 2000. Applicants also claim priority under35 U.S.C. §365 of PCT/AT01/00096 filed Apr. 3, 2001. The internationalapplication under PCT article 21(2) was not published in English.

The invention relates to a method of continuously controlling andtracking a position of a welding torch and a welding head relative to aweld seam to be produced on a workpiece, whereby the welding torch,spaced at a distance from a workpiece and the welding seam, effects apendulum motion superimposed on its linear welding motion, during whichstate variables, in particular an ohmic resistance or a current and/or avoltage, are detected as they vary in time, the detected actual valuesbeing used to determine the lateral deviation of the welding torch fromthe weld seam, in particular the welding centre line, and/or the heightof the welding torch above the workpiece and weld seam in order tocontrol and track the position of the welding torch, and a method ofgenerating a signal enabling a position of a welding torch and a weldinghead to be continuously controlled and tracked.

Patent specification DE 43 17 178 A discloses a method of continuouslycontrolling the position of a welding torch and welding head relative toa weld seam to be produced by the welding head, whereby the weldinghead, spaced at a distance above the weld seam, effects a pendulummotion superimposed on its linear welding motion, whilst the ohmicresistance of the arc or a similar variable, which varies over time, ismeasured. A measure of the height of the welding head above the weldingseam and the lateral deviation of the welding head from the weld seamare respectively derived from the signal and input at the controlcircuit. The measurement values and signals for the pendulum half-waveson the right-hand side of the weld seam are separated from themeasurement values and signals for the pendulum half-waves on theleft-hand side of the weld seam. One group of signals thus obtained isentered at the control circuit as a height actual value and the othergroup signals thus obtained is entered as a lateral actual value.

Also known from patent specification DE 38 44 124 A1 is an automaticcopying method for a welding torch in an arc welding robot, whereby,when welding a fillet joint, welding is effected at an oscillationmid-point by the arc welding robot with a consumable electrode, whilstthe welding torch is displaced in a weaving motion across a weld joint,in other words in a pendulum motion. With this method, the integratedcurrent values of the two oscillating ends are compared with anintegrated current value of an oscillation mid-point in order to preventthe fillet welding line from moving against a top plate of the workpieceand thereby correct the position of the welding torch depending on thedeviation.

Patent specification DE 26 45 788 A1 describes a method and a device formechanically guiding a welding head, whereby the integral weldingcurrent of the periodically oscillating welding torch or welding head ismeasured at the two reversing points of the pendulum motion,irrespective of the number of wire electrodes melted off by the weldingtorch, and the welding head is guided at the centre of the weld line ina known manner by comparing them.

Patent specification U.S. Pat. No. 5,780,808 A describes an automatedarc welding method for welding with a robot, whereby the arc current issensed in order to derive signals for the position of the welding torchabove the workpiece. Not only does this make it possible to position thework-piece horizontally, it also allows the position of the weldingtorch relative to the weld line to be adjusted if the workpiece is in aninclined position. The position of the weld line centre is determined insuch a way that the welding torch is guided relative to the weld linecentre on the basis of the arc current.

Another method of controlling the position of a welding torch relativeto a welding line is known from patent specification U.S. Pat. No.4,906,814 A1, whereby signals are derived from the sensed arc currentand used to determine the position of the welding torch. To this end,the welding torch again effects a pendulum motion and the varying statesof the arc are taken into account.

The disadvantage of the known methods described above is that additionalmeasuring equipment is needed in order to detect and measure the statevariables and has to be connected by cables to the relevant elements onthe welding torch in order to sense the state variables of the weldingprocess, after which the sensed signals are forwarded to the robotcontroller for a desired/actual comparison.

The underlying objective of the invention is to propose a method ofcontinuously controlling and tracking a position of a welding torch andwelding head relative to a weld seam to be produced on a workpiece and amethod of generating a signal whereby measurements can be sensed and thequality of the signal for controlling positioning improved without theneed for additional external components, such as measuring apparatus forexample.

This objective is achieved by the invention due to the fact that theactual values dependent on processing state are evaluated by the controlsystem of the welding device or at least another control system in thewelding device, whereupon the control system transmits at least one orseveral correction value(s) for the position of the welding torch to adevice or system linked to the welding device, in particular a weldingrobot or robot system. The advantage of this is that because the entireevaluation is performed by only one device, in particular by the weldingdevice, delays in the time needed to run data exchanges can beminimised. Another advantage resides in the fact that the welding devicemakes allowance for unforeseen external process influences or processdisruptions when establishing the positioning values, preventing themfrom disrupting the welding process and affecting the positionadjustments.

The objective is also achieved by the invention due to the fact that,during periodically recurring process phases of a welding process, themeasurement value detection routine for at least one measurement signal,in particular to detect the state variable, is run at specified instantsand/or states during the periodically recurring process phases of thewelding process. The advantage of this approach is that the measurementvalue detection routine can be correlated with the welding process,enabling the individual welding state during the welding process to betaken into account when generating the signals and actual values neededfor positioning purposes. One particularly significant advantage is thatby using a programme data bank, welding process parameters for processphases can be correlated with parameters for measurement signals, as aresult of which optimum measuring results will always be obtained forthe most varied of process phases, enabling external influences on thestate variables of the welding process to be compensated. Also ofadvantage is the fact that several measurement signals can be grouped toobtain a common signal, which significantly improves the quality of thesignal.

The invention will be described in more detail with reference to theillustrated embodiments.

Of these:

FIG. 1 is a schematic diagram of a welding machine and welding device;

FIG. 2 is a schematic diagram of how a welding torch is guided relativeto a weld line on a workpiece;

FIG. 3 is a simplified, schematic diagram plotting the signal used todetermine the position of the welding torch;

FIG. 4 is a simplified, schematic diagram of a welding process run by awelding device;

FIG. 5 is a simplified, schematic diagram showing another weldingprocess of the welding device;

FIG. 6 is a simplified, schematic diagram showing part of a processphase of the welding process illustrated in FIG. 4 or 5.

Firstly, it should be pointed out that the same reference numbers areused for common parts of the individual embodiments.

FIG. 1 illustrates a welding device 1 for a whole range of weldingprocesses, e.g. MIG-MAG welding and TIG welding or electrode weldingprocesses. Clearly, the solution proposed by the invention may be usedwith a current source or welding current source.

The welding device 1 has a current source 2 with a power component 3, acontrol system 4 and a switching element 5 co-operating with the powercomponent 3 and control system 4. The switching element 5 or the controlsystem 4 is connected to a control valve 6 incorporated in a supply line7 for a gas 8, in particular an inert gas such as CO₂, helium or argonand such like, running between a gas storage 9 and a welding torch 10.

Furthermore, a wire feed device 11 such as commonly used for MIG-MAGwelding may also be activated via the control system 4 in order to feeda welding wire 13 from a supply reel 14 through a wire guide line 12into the region of the welding torch 10. Clearly, the wire feed device11 could also be integrated in the welding device 1, in particular inthe basic housing, in a manner known from the prior art, rather thanused as an add-on device as illustrated in FIG. 1.

The current needed to strike an arc 15 between the welding wire 13 and aworkpiece 16 is fed via a welding line 17 from the power component 3 ofthe current source 2 to the welding torch 10 and the welding wire 13,the workpiece 16 to be welded also being connected to the welding device1, in particular to the current source 2, via another welding line 18 sothat a current circuit can be established across the arc 15.

In order to cool the welding torch 10, the welding torch 10 can beconnected via a cooling circuit 19, with an integrated flow indicator20, to a fluid container, in particular a water container 21, so thatthe cooling circuit 19, in particular a fluid pump used to pump theliquid contained in the water container 21, can be activated when thewelding torch 10 is switched on, thereby enabling the welding torch 10and the welding wire 13 to be cooled.

The welding device 1 also has an input and/or output device 22, by meansof which a whole range of settings can be entered for welding parametersand operating modes of the welding device 1. The welding parametersentered at the input and/or output device 22 are then forwarded to thecontrol system 4, from where they are applied to the individualcomponents of the welding system and the welding device 1.

In the embodiment illustrated as an example here, the welding torch 10is also connected to the welding device 1 and the welding system bymeans of a hose pack 23. The individual lines from the welding device 1to the welding torch 10 are disposed in the hose pack 23. The hose pack23 is connected by means of a connector device 24, known from the priorart, to the welding torch 10, whilst the individual lines in the hosepack 23 are connected to the individual contacts of the welding device 1by means of connecting sockets and plug connectors. To relieve tensionon the hose pack 23, the hose pack 23 is connected via atension-relieving device 25 to a housing 26, in particular the basichousing of the welding device 1.

FIGS. 2 and 3 illustrate a process sequence for controlling and trackinga position of the welding torch 10 and welding head, during which thewelding torch 10 is guided along a welding line 27 by means of a deviceor system, in particular a robot system or a welding robot.

To this end, a profiled weld line 27 is illustrated as an example inFIG. 2, comprising two workpieces 28, 29 placed in abutment with oneanother and having matching profiled surfaces which form a V-shaped weldline 27 or weld seam in conjunction with one another. To form a weldingbead in the weld line 27, the schematically illustrated welding torch 10is positioned above the workpieces 28, 29.

The welding torch 10, spaced at a distance apart from the workpieces 28,29 and weld seam, effects a pendulum motion which is superimposed on itslinear welding motion, indicated by arrow 30, during which statevariables, in particular an ohmic resistance or a current and/or avoltage, are detected as they vary in time, i.e. the welding currentand/or welding voltage or the resulting resistance between the weldingtorch 10 and the workpiece 28, 29 are detected. The pendulum motion isshown by broken lines 31 in FIG. 2 to illustrate the way in which thewelding torch 10 is displaced by the robot system. This displacement ofthe welding torch 10 is programmed in the robot system in a manner knownfrom the prior art and such a displacement sequence can be produced by arobot controller working through the programme. At the same time, asmentioned above, at least one state variable of the welding process isdetected at predetermined instants and processed by the robot system forthe purpose of positioning and controlling or tracking the welding torch10, i.e. the current flowing between the welding torch 10 or a contactpipe and the workpiece 28, 29 is measured once a welding process isinitiated so that corresponding actual values and signals for theposition of the welding torch relative to the weld line 27 or weld seamcan be derived by the robot system.

A signal of this type is plotted in FIG. 3, the maximum valuesindicating the weld line centre and the minimum values indicating themaximum lateral deviation to the left or right. The plotted signal ismade up of an individual signal 32 having varying values and actualvalues, as schematically illustrated in a part-region of FIG. 3,although the individual actual values of the signal 32 are processedimmediately they are detected by the robot system for position controland position correction purposes. However, in order to be able to run aposition-correcting process of this type, a calibration process isinitially run, usually at the start of a welding process. This enables aseam centre with corresponding desired values to be determined so thatthe detected actual values corresponding to the values of the signal 32can be compared subsequently, during the welding process, with thestored and determined desired values enabling the position of thewelding torch 10 to be controlled during the welding process, i.e. therobot system for controlling and tracking the position of the weldingtorch 10 will be able to derive from the detected actual value andsignals the lateral deviation of the welding torch 10 relative to theweld seam, in particular relative to the welding line centre, and/or theheight of the welding torch 10 above the workpiece 28, 29 and weld seam.

Process sequences of the type described above are already known from theprior art, for example patent specifications DE 43 17 178 A1, DE 38 44124 A1, DE 26 45 788 A1, U.S. Pat. No. 5,780,808 or U.S. Pat. No.4,906,814 A, and the way in which the signals 32 and actual valuesrelating to position are determined will not be discussed in furtherdetail here. During these process sequences, an additional measuringdevice is used to sense the measurement values, i.e. correspondingmeasurement points or measurements spots at which the state variables ofthe welding process will be sensed, usually in the region of the weldingtorch 10, are fixed and the measurement points are linked by cables toan evaluating device in the robot system so that it can producecorresponding actual values for the robot controller.

The new method of determining positioning and producing the signals 32and actual values defining the position of the welding torch 10 will nowbe described with reference to FIGS. 4 to 6. To this end, FIGS. 4 and 5plot the current of an entire welding process 33, for example a pulsewelding process, which, in the embodiment described here, lasts for atotal duration 34.

At the start of this welding process 33, a start pulse 35 is shown,indicating ignition of the arc 15, and, once the arc 15 has beenignited, the current level is reduced to a basic current 36 formaintaining the arc 15. The basic current 36 is kept constant for apre-settable period 37. Within this period 37, the robot system will nowhave the opportunity to run a calibration process, i.e. before startingthe actual welding process 33, a zero calibration is run and the sensedor detected signals 32 or actual values are stored as reference valuesor desired values. Clearly, it would also be possible to run thecalibration process during the actual welding process 33.

When the period 37 has elapsed, the welding process 33 proper isinitiated by the welding device 1 or a control system 4 in the weldingdevice 1 (see FIG. 1), made up of several periodically recurring processphases 38, i.e. the welding process 33 is made up of individual sectionsor process phases 38. In the embodiment illustrated as an example here,this welding process 33 is a pulse welding process, i.e. with everypulse 39, a welding droplet is detached from the welding wire 13 (seeFIG. 1). The pulse welding process is therefore made up of a pulse phase40 and a pause phase 41 at a pulse period 42 and several such pulseperiods 42 occur one after the other during a welding process 33. Thewelding process 33 illustrated in FIG. 4 is operated with a pulse period42 which remains constant, whereas in FIG. 5, there is a change in thepulse period 42, i.e. the period duration 44, at an instant 43. Toprovide a clearer illustration, FIG. 6 shows a process phase 38 of thewelding process 33, in other words a single pulse period 42 in thisembodiment.

As described in particular with reference to FIG. 2, for the purposes ofthe method proposed by the invention and with a view to continuouslycontrolling and tracking the position of the welding torch 10 andwelding head relative to a weld seam to be produced on the workpiece 28,29, the welding torch 10, spaced at a distance from the workpiece 28, 29and the weld seam, effects a pendulum motion which is superimposed onits linear welding motion, indicated by arrow 30, during which timestate variables which vary over time, in particular an ohmic resistanceor a current and/or a current, are detected.

Unlike the methods known from the prior art, the measurement values, inparticular the state variables, needed to produce a signal 32 or theactual value are detected in the welding device 1, in particular at theoutput terminals of the welding device 1. Given that the measurementvalues and the signals 32 are produced by the welding device 1, inparticular by the control system 3 of the welding device 1, it will bepossible to make use of the monitoring systems and the measuringinstruments or units used to control the welding process 33, therebyobviating the need for any additional external measuring system. Thedata and actual values generated by the welding device 1 are thentransmitted to the robot controller for position-tracking purposes.Another option would be to run a two-way data exchange between thecontrol system 3 of the welding device 1 and the robot controller sothat corresponding control commands can be applied to or taken intoaccount by the robot controller when generating the signals 32 and theactual values.

For the purpose of the positioning method proposed by the invention, adistinction is made between different data sets relating to the positionof the welding torch 10, i.e. on the one hand between data to beprocessed in the welding device 1 and data which will be transmitted tothe robot and the robot controller. The data and actual values that aredetermined, computed or processed in the welding device 1 are thendesignated as measurement signals 45 and the data and actual valuesforwarded by the welding device 1 are designated as signals 32.

Since detection of the data and the measurement signals is controlledfrom the welding device 1, the measurement value detection routine canbe correlated with the welding process 33, i.e. depending on theperiodically recurring process phases 38 of a welding process 33 as awhole, the detection routines for the measurement values of at least onemeasurement signal 45, in particular the detection routines for thestate variable, can be run at fixed instants 46 and/or states of theperiodically recurring process phases 38 of the welding process 33. Thedata and actual values for the position of the welding torch 10 can bedetected in the welding device 1 on the basis of the measurement valuesof the state variables due to the fact that these measurement values areequivalent to the measurement values at the welding torch 10, i.e. anarc length or the distance of a contact pipe between the welding torch10 and the workpiece 16, 28, 29 need not be detected directly at thewelding torch 10, but can be derived directly from the state variablesin the welding device 1. The measurement signals 45 of the statevariables sensed in the welding device 1 and/or at the output terminalsof the welding device 1 therefore correspond to a length of the arc 15or a contact pipe distance from the weld seam or weld line 27, i.e. theprocess-state dependent actual values or measurement signals 45 of thestate variables sensed in the welding device 1 represent an arc lengthequivalent and/or an equivalent of the contact pipe length from the weldseam and constitute a signal equivalent to an arc length and/or acontact pipe length.

Another advantage of using the data that is available in the weldingdevice 1 for the welding process 33 is that no additional measuringequipment and hence no wiring is necessary, as is the case with themethods known from the prior art, thereby preventing any faultyconnection of sources. One significant advantage is the fact that theinternal data of the welding device 1 can be directly correlated withthe welding process 33, so that any variations in the welding process 33during set-up and/or adjustment as well as any disruptions can be takeninto account when determining the measurement values, i.e. the instantsor states during which the detection routines of the measurement signals45 are run can be adapted whenever the process phases of the weldingprocess 38 are changed.

In the embodiment illustrated as an example here, the measurement valuesare detected during pulse welding at fixed instants 46 or duringspecific process phases 38 of the pulse period 42, in particular a pulsephase 40 and/or a pause phase 41 and/or other processes states, e.g.during a short circuit etc., or during the entire period or acombination of the above. Accordingly, several measurement signals 45can be generated during a process phase 38 or during a pulse period 42at different instants 46 and/or states.

In order to render the process of determining the measurement values andthe measurement signals 45 transparent in respect of a process phase 38,the detection instants are indicated by broken lines in FIGS. 4 to 6. Atthese instants 46, the state variables are being sensed, i.e. thecurrently prevailing values of the welding current and/or the weldingvoltage in particular are detected and stored as a measurement signal 45or actual value and will subsequently be processed by a control system 3in the welding device 1 to generate a signal 32, i.e. the signalequivalent to the arc length and/or the signal equivalent to the contactpipe length will be forwarded to an external device or system, inparticular a robot system.

Various different evaluation methods may then be used. One option is totransmit the generated measurement signals 45 directly to the robotcontroller as signals 32 or, alternatively, several measurement signals45 may be grouped in a single signal 32. In this case however, it ispreferable to group only those measurement signals 45 of one processphase 38, in other words a pulse period 42.

The control system 3 of the welding device 1 may use various methods togroup several measurement signals 45 into a single signal 32. Onepossible option, for example, is to compute a mean value or take accountof the proportion of individual measurement signals 45 on a percentagebasis or sum the individual measurement values 45. The essential factoris that a signal 32 is generated that is understandable to a robotcontroller, in particular a signal equivalent to an arc length and/or acontact pipe length.

The key advantage of grouping several measurement signals 45 into onesignal 32 is that accuracy can be very much improved and, beingcorrelated to a process phase 38 of the welding process 33, the statesof the welding process 33 can also be taken into account.

Another way of groping several measurement signals 45 is to definemeasurement signal parameters in a programme data bank, defining theproportions of individual measurement signals 45, in particular theindividual measurement signals 45 at the different instants 46 duringthe welding process 33 or in the process phase 38 needed to compute andgenerate the signal 32, in particular the signal equivalent to the arclength and/or contact pipe length. With this option, the parameters forthe measurement signals can be correlated by the programme data bankwith the welding process parameters of the process phases 38 and awelding process controller. By preference, the programme data bankoperates with a fuzzy logic parameter structure.

Using a programme data bank and allocating parameters for measurementsignals means that the most varied of parameters, such as proportions ona percentage basis, priorities and valencies, can be assigned to thedifferent measurement signals 45 and actual values sensed with a view tocomputing the signal 32, thereby enabling the quality of the signal 32computed or generated to be significantly improved. Another advantage isthat a definition of different process phases 38 can be run in theprogramme data bank where the parameters for the measurement signals arecorrelated with the welding parameters so that specific measurementsignals 45 for generating the signal 32 will always be applied whenevera process phase 38 of this type is selected and/or retrieved, i.e.different instants 46 or states for detecting the state variables can bedefined for different process phases 38 or the valencies or proportionsof the individual actual values and measurement values 45 can bechanged.

As a result, only those measurement signals 45 which are guaranteed todetect the state variables will be applied when computing the signal 32,so that any sections of a process phase 38 which carry faults or aredisruptive can be gated out.

As may be seen from the embodiments illustrated as examples here, twomeasurement signals 45 are detected within a pulse period 42. Naturally,it would also be possible to generate several measurement signals 45during a process phase 38. This being the case, the first measurementsignal 45 will be determined in the pulse phase 40 and the secondmeasurement signal 45 in the basic current phase 41. A single signal 32will then be generated from these two measurement signals 45 by acontrol system 3 and transmitted to the robot controller. Themeasurement signals 45 will always be detected at the same instants 46of a pulse period 42. This also offers the possibility of varying theperiod duration 44 of one or more pulse periods 42, as illustrated inFIG. 5, starting from the instant 43, in which case the instants 46 atwhich the measurement signals 45 are detected will be changedaccordingly, i.e. the instants 46 will vary as a proportion of the pulseperiod 42 and the period duration 44, in other words of the processphase 38, so that the detection routines will always be run at the samestate of the process.

To be absolutely clear as to how this method differs from the prior art,the detection instants 47 used by the known systems have been shown bydotted-dashed lines in FIGS. 4 and 5. Because the known methods offer noway of establishing a correlation with the welding process 33, thedetection instants 47 are defined and fixed, so that once the weldingprocess 33 has been initiated, a measurement value detection routine isrun on expiry of a fixed, pre-set period 48. As may be seen from FIG. 4,if the process phases 38 remain unchanged, this is always run during aspecific state of the welding process 33 and the values of the detectedstate variables will therefore not vary very much in relation to oneanother, making it possible to operate a position control via the robotcontroller on the basis of the state variables. However, this is barelyfeasible in practice because disruptive influences, changes ofmaterials, supply fluctuations, etc. affect the welding process 33 andthe individual process phases 38 of the welding process 33 have to berepeatedly controlled and adjusted by the welding device 1 (see FIG. 1).

If, however at least one process phase 38 of the welding process 33changes within a period duration 44, as illustrated with effect frominstant 43 in FIG. 5, the individual detection instants 47 are notchanged in the methods known from the prior art so that a situation willnow arise in which these detection instants 47 coincide with a wholeseries of different states of the pulse period 42 and the process phases38. Consequently, the measurement results will always be different, forexample because the detection routine will be run at one point in thepulse phase 40 and another time in the basic current phase 41, whichmeans that the values of the state variables will deviate from oneanother significantly every time, making it impossible to determine theexact position for the welding torch 10, and the robot controller willbe unable to correct the position on a continuous basis.

Due to the fact that detection of the state variables is correlated tothe welding process 33 in the method proposed by the invention, theinstants 46 or states at which the measurement value detection routinesfor the measurement signals 45 are run will be adapted to new processphases 38 of the welding process 33 whenever these are changed, asillustrated in FIG. 5, which means that measurements will always betaken in the same process phase 38. Consequently, large deviations willnever occur and the position of the welding torch 10 with respect to thewelding line 27 can always be detected with total reliability. Anothersignificant aspect is the fact that when the measurement signals 45 areevaluated, the states of the welding process 33 can be taken intoaccount, enabling corrections to be applied accordingly, i.e. if onemeasurement is taken in the pulse phase 40 and one measurement is takenin the pause phase 41, these two measurement signals 45 can bereconciled with one another because the control system 3 of the weldingdevice 1 is always kept informed and aware of the current states andprocess phases 38 of the welding process 33. This might be necessaryinsofar as a higher value always prevails in the pulse phase 40 than inthe pause phase 41 and adaptation will then be possible using anappropriate evaluation mode, enabling a corresponding signal 32 to begenerated for the robot controller. Naturally, it would also be possibleto group several measurement signals 45 from different process phases 38in one signal 32.

It may therefore be said that the measurement signals 45 determined andgenerated during a periodically recurring process phase 38, inparticular a pulse period 42, are processed to generate one signal 32 bymeans of an evaluating device in the welding device 1 or the controlsystem 3 in the welding device 1, so that the instants 46 or the statesat which the measurement value detection routines for the measurementsignals 45 are run will be adapted to new process phases 38 of thewelding process 33 whenever these are changed. The signals 32 and actualvalues for positioning purposes therefore correspond to the signals 32described with reference to FIG. 3, and these signals 32 can thereforebe used for position control purposes and forwarded to an externaldevice or system.

Clearly, the state variables could also be sensed directly at thewelding torch 10, in which case the sensed measurement signals 45 wouldbe transmitted from the welding torch 10 to the welding device 1, inparticular to the control system 3 via a field bus or control lines, toenable the signals 32 to be generated by the welding device 1 or fromthe control system 3 of the welding device 1 and hence correlated to thewelding process 33. Another option is to detect the state variablesdirectly on the welding torch via measuring lines. If using this type ofmeasuring method, however, care must be taken to ensure that the sensedactual values and measurement signals 45 are correlated with and linkedinto the welding process 33 and the process phase 38.

Naturally, it would also be possible to use the method described abovefor other welding processes. Accordingly, in a short arc weldingprocess, the measurement values would be detected during short circuitwelding at fixed instants or during fixed states of the process,depending on the short circuit frequency, and the short circuitfrequency used as a measurement value, which will again enable severalmeasurement signals 45 to be determined and then converted to a signal32.

The significant aspect of the different individual welding processes isthat the measurement values are always detected in correlation with thewelding process 33 and because detection of the measurement valuesand/or the evaluation process is correlated with the welding process 33,any changes in the welding process 33 can be taken into account.Accordingly, changes can be made to the welding process 33 independentlyor can be programmed using a stored welding programme. This will alsoallow the current strength to be increased due to an increase inmaterial with effect from a specific instant and a specific flag so thatthe values sensed by the measurement value detection routines and theinstants 46 can be adjusted to the new settings and parameters.

In yet another option, because the signals 32 are generated by thewelding device 1 and by the control system 4 of the welding device 1,the process-dependent signals 32 and actual values can also be evaluatedby the control system 4 of the welding device 1 or at least one othercontrol system in the welding device 1, in which case the control system4 will transmit one or several correction value(s) for the position ofthe welding torch 10 to the device or system connected to the weldingdevice 1, in particular a welding robot or a robot system, i.e. the datarelating to the spatial position of the welding torch 10 will betransmitted directly from the welding device 1 or the control system 4,in which case the robot system will merely have to act on thepositioning information. There will no need for an evaluation in therobot system because the position is determined exclusively by thewelding device 1 in this instance and the desired/actual comparisontakes place in the welding device 1.

To this end, it is of advantage to run a two-way data exchange betweenthe welding device 1 and the robot system, in which case the requisitedirectional instructions for the sequence of motions to be performed bythe welding torch 10 can be provided from the welding device 1 and thecontrol system 4 accordingly. Consequently, a direction signal for thedisplacement of the welding torch 10 can be transmitted to the weldingdevice 1, in particular the control system 4, from the robot system.When the process is initiated, the desired values for the spatialposition of the welding torch 10 and welding head are preferablytransmitted to the welding device 1, in particular the control system 4,and, once the signals 32 have been generated, a desired/actualcomparison can be run. Accordingly, the entire evaluation will be run bythe welding device 1 and the settings for displacement of the robot armof the robot system determined by the welding device 1.

Naturally, as part of the process of generating a signal or continuouslycontrolling and tracking a position of the welding torch 10 and weldinghead relative to a weld seam to be produced on a workpiece 16, 28, 29,other parameters of the welding device 1 and the robot system, such asthe wire feed rate, welding speed, etc., can also be taken into account.

Another possibility is to run the method described above from anexternal control system. In this case, care must be taken to ensure thatthe control system can be linked into the welding process 33 so that themeasurement value detection routines for the measurement signals 45 willalways be run depending on a process phase 38 of the welding process 33.The external control system can then assume the task of generating thesignal 32 from the measurement signals 45 and running the entireevaluation to determine the position of and guide the welding torch 10.

Finally, it should be pointed out that individual parts and featuresillustrated the embodiments described above are shown on adisproportionately large scale in the drawings in order to provide aclear understanding of the solution proposed by the invention.Individual parts and aspects of the combinations of features describedabove in respect of the individual embodiments may be used incombination with other individual features from the other embodimentsand construed as independent solutions of the invention.

List of Reference Numbers

-   1 Welding device-   2 Current source-   3 Power component-   4 Control system-   5 Switching element-   6 Control line-   7 Supply line-   8 Gas-   9 Gas storage-   10 Welding torch-   11 Wire feed device-   12 Wire guide line-   13 Welding wire-   14 Supply reel-   15 Arc-   16 Workpiece-   17 Welding line-   18 Welding line-   19 Cooling circuit-   20 Flow indicator-   21 Water container-   22 Input and/or output device-   23 Hose pack-   24 Connector device-   25 Tension-relieving device-   26 Housing-   27 Weld line-   28 Workpiece-   29 Workpiece-   30 Arrow-   31 Line-   32 Signal-   33 Welding process-   34 Total duration-   35 Start pulse-   36 Basic current-   37 Period-   38 Process phase-   39 Pulse-   40 Pulse phase-   41 Pause phase-   42 Pulse period-   43 Instant-   44 Period duration-   45 Measurement signal-   46 Instant-   47 Detection instant-   48 Period

1. Method of continuously controlling and tracking a position of awelding torch and a welding head relative to a weld seam to be producedon a workpiece, wherein the welding torch is spaced at a distance apartfrom the workpiece and the weld seam, and effects a pendulum motionwhich is superimposed on its linear welding motion, electric statevariables are detected as they vary in time, the lateral deviation ofthe welding torch from the weld seam, in particular from the weld seamcenter, and/or the height of the welding torch above the workpiece andweld seam being derived from the detected actual value signals in orderto control and track the position of the welding torch, characterised inthat process-dependent actual values are evaluated by a control systemof the welding device or at least one other control system in thewelding device, whereupon the control system transmits one or morecorrection value(s) relating to the position of the welding torch to adevice or system connected to the welding device, in particular awelding robot or a robot system, and a measurement value is detectedduring specific process phases of a pulse period during pulse welding,several measurement signals being generated during a pulse period, andspecific process phases during the pulse period are detected solely onthe basis of the electric state variable value signals generated in thewelding device during the welding process.
 2. Method as claimed in claim1, characterised in that the measurement signals are detected at theoutput terminals of the welding device.
 3. Method as claimed in claim 1,characterised in that a measurement value detection is run during apulse phase and/or a basic current phase and/or another process state,such as during a short circuit, or the entire period or a combinationthereof.
 4. Method as claimed in claim 1, characterised in that ameasurement value detection during short arc welding is run depending onthe short circuit frequency and the short circuit frequency constitutesthe measurement value.
 5. Method as claimed in claim 1, characterised inthat the actual value signals of the detected electric state variablesrepresent an arc length equivalent and/or a contact pipe lengthequivalent to the weld seam.
 6. Method as claimed in claim 1,characterised in that the electric state variables are detected directlyat the welding torch and the sensed actual value signals are transmittedfrom the welding torch to the control system of the welding device via afield bus or control lines.
 7. Method as claimed in claim 1,characterised in that the electric state variables are detected directlyat the welding torch via measuring lines.
 8. Method as claimed in claim1, characterised in that the electric state variables are adapted tochanged process phases of the welding process for the detection of theactual value signals.
 9. Method as claimed in claim 1, characterised inthat a zero calibration is run before the start of the welding processand the detected actual value signals are stored as reference values ordesired values.
 10. Method as claimed in claim 1, characterised in thatthe measurement signals produced or generated during periodicallyrecurring process phases, in particular the pulse period, are processedto generate the actual value signal by an evaluating device in thecontrol system of the welding device.
 11. Method as claimed in claim 1,characterised in that an arc length equivalent and/or contact pipelength equivalent signal computed from the electric state variables isforwarded to an external device or system.
 12. Method as claimed inclaim 1, characterised in that measurement signal parameters defined ina program data bank define proportions of individual measurement signalsfor computing the signal, in particular the arc length equivalent and/orcontact pipe length equivalent signal.
 13. Method as claimed in claim 1,characterised in that a program data bank is based on a fuzzy logicparameter structure.
 14. Method as claimed in claim 1, characterised inthat a direction signal for the displacement of the welding torch istransmitted from a robot system to the control system of the weldingdevice.
 15. Method as claimed in claim 1, characterised in that thedesired values for the spatial position of the welding torch and weldinghead are transmitted by a robot system to the control system of thewelding device, in particular the control system.
 16. Method as claimedin claim 1, characterised in that the welding device assumes the role offixing the settings for the displacement of the robot arm of a robotsystem.
 17. Method of generating a signal for continuously controllingand tracking a position of a welding torch and welding head relative toa weld seam to be produced on a workpiece, wherein the welding torch isspaced at a distance apart from the workpiece and the weld seam, andeffects a pendulum motion which is superimposed on its linear weldingmotion, electric state variables are detected as they vary in time, thelateral deviation of the welding torch from the weld seam, in particularfrom the weld seam center, and/or the height of the welding torch abovethe workpiece and the weld seam being derived from the detected actualvalue signals in order to control and track the position of the weldingtorch, characterised in that, depending on periodically recurringprocess phases of a welding process, a measurement value detection forat least one measurement signal of the detected electric state variableis run at states of the periodically recurring process phases of a pulseperiod of the welding process, measurement signal parameters are definedin a program data bank, which are correlated with welding processparameters of the process phases and a welding process controller, andthe process phases during the pulse period are detected solely on thebasis of the electric state variable value signals generated in thewelding device during the welding process.
 18. Method of continuouslycontrolling and tracking a position of a welding torch and a weldinghead relative to a weld seam to be produced on a workpiece, wherein thewelding torch is spaced at a distance apart from the workpiece and theweld seam, and effects a pendulum motion which is superimposed on itslinear welding motion, electric state variables are detected as theyvary in time, the lateral deviation of the welding torch from the weldseam, in particular from the weld seam center, and/or the height of thewelding torch above the workpiece and weld seam being derived from thedetected actual value signals in order to control and track the positionof the welding torch, characterised in that process-dependent actualvalues are evaluated by a control system of the welding device or atleast one other control system in the welding device, whereupon thecontrol system transmits one or more correction value(s) relating to theposition of the welding torch to a device or system connected to thewelding device, in particular a welding robot or a robot system, and ameasurement value is detected at fixed points in time, the fixed pointsin time are detected solely on the basis of the electric state variablevalue signals generated in the welding device during the weldingprocess, and an arc length equivalent and/or contact pipe equivalentsignal computed from the electric state variables is forwarded to anexternal device or system.
 19. Method of generating a signal forcontinuously controlling and tracking a position of a welding torch andwelding head relative to a weld seam to be produced on a workpiece,wherein the welding torch is spaced at a distance apart from theworkpiece and the weld seam, and effects a pendulum motion which issuperimposed on its linear welding motion, electric state variables aredetected as they vary in time, the lateral deviation of the weldingtorch from the weld seam, in particular from the weld seam center,and/or the height of the welding torch above the workpiece and the weldseam being derived from the detected actual value signals in order tocontrol and track the position of the welding torch, characterised inthat, depending on periodically recurring process phases of a weldingprocess, a measurement value detection for at least one measurementsignal of the detected electric state variables is run at fixed instantsof the welding process, measurement signal parameters are defined in aprogram data bank, which are correlated with welding process parametersof the process phases and a welding process controller, the fixedinstants are detected solely on the basis of the electric state variablevalue signals generated in the welding device during the weldingprocess, and an arc length equivalent and/or contact pipe equivalentsignal computed from the electric state variables is forwarded to anexternal device or system.